Cyclotron Resonance Study Research Articles

Cyclotron Resonance Study of Monolayer Graphene under Double Moiré Potentials.

We report the first cyclotron resonance study of monolayer graphene under double-moiré potentials in which the crystal axis of graphene is nearly aligned to those of both the top and bottom hexagonal boron nitride (h-BN) layers. Under mid-infrared light irradiation, we observe cyclotron resonance absorption with the following unique features: (1) cyclotron resonance magnetic field BCR is entirely different from that of nonaligned monolayer graphene, (2) BCR exhibits strong electron-hole asymmetry, and (3) splitting of BCR is observed for |ν| < 1, with the split maximum at |ν| = 1, resulting in eyeglass-shaped trajectories. These features are well explained by considering the large bandgap induced by the double moiré potentials, the electron-hole asymmetry in the Fermi velocity, and the Fermi-level-dependent enhancement of spin gaps, which suggests a large electron-electron correlation contribution in this system.

LO-phonon-assisted cyclotron resonance in a special asymmetric hyperbolic-type quantum well

This paper is devoted to the study of the phonon-assisted cyclotron resonance (PACR) in a special asymmetric hyperbolic-type (SAsH) quantum well, in which the two-photon absorption process and the electron–LO-phonon interaction have been included. The PACR effect has been investigated through considering the magneto-optical absorption coefficient (MOAC) and the full-width at half maximum (FWHM). Our results showed that it is better to investigate MOAC and FWHM when the a-parameter value of the quantum well is in the range from 9.72 nm to 37.14 nm. The threshold energy decreases non-linearly with the a-parameter but increases linearly with the magnetic field. The resonant peaks caused by the emission phonon process are observed significantly. MOAC gives red-shift with the increase of a-parameter, gives blue-shift with the rise of magnetic field, but unchanged with the change of temperature, while MOAC's intensities increase with the increase of these three parameters. FWHM decreases with the rise of a-parameter but increases with the growth of temperature and magnetic field in both the emission and absorption phonon processes.

Residual-Oil Zone: Paleo-Oil Characterization and Fundamental Analysis

Summary In most reservoirs around the world, paleo oil exists below the free-water level (FWL) and is considered residual oil to natural/geological waterflood. This nontrivial resource of residual oil will not flow by primary- or secondary-recovery means but requires carefully designed enhanced-oil-recovery (EOR) methods to mobilize it. To date, there is no detailed analysis of paleo oil in the literature simply because it is difficult to obtain a reservoir sample. This study provides a comprehensive paleo-oil analysis for samples obtained from reservoir sponge cores. The oil in the sponge core was extracted, analyzed, and compared with main-pay-zone (MPZ) oil. Critical data have been unveiled on paleo-oil characterization through fundamental studies on oil quality, fingerprint, filling history, available hydrocarbon components and compounds, and molecular-level characterization. It was found that the global composition and overall quality of paleo oil are very similar to those of the MPZ oil. However, the differences between the two oils were only apparent when the study was extended further to include molecular-level analysis and available hydrocarbon components and compounds. These differences may define the appropriate EOR methods to mobilize this oil and explain trapping mechanisms caused by fluid properties. Gas-chromatography (GC) studies revealed that paleo-oil extracts have the same pristane/phytane ratio as the MPZ oil, suggesting that they are of the same origins and share the same source rock. Further analysis showed a good match of the terpane biomarkers between paleo-oil extracts and MPZ oil but with slightly lower maturity levels. Paleo-oil quality was compared with MPZ oil by use of pyrolytic oil-productivity index (POPI) analysis which indicated the same °API range as the MPZ oil and the same light volatile, thermally distilled, and cracked components. Paleo and MPZ oils were also analyzed with low-field nuclear magnetic resonance (NMR) to qualitatively test the similarity of the oil components and to measure their apparent viscosities. Both oils have shown very comparable viscosity measurements and NMR signatures. The simulated distillation analysis showed that lighter components in paleo oil are less abundant than in MPZ oil, whereas medium-to-heavy components are relatively similar. A Fourier transform ion cyclotron resonance (FT-ICR) study, which zoomed into the heavier components, revealed that paleo oil has less aromaticity than MPZ oil and lacks aromatic sulfur and disulfur compounds, a negligible amount of nitrogen compounds, and no resin-type components. This study provides in-depth information about oil extracted from the residual-oil zone (ROZ), which does not flow by primary or secondary recovery means. To our knowledge, there is no available information in the literature that explains the components, compounds, quality, and behavior of this oil because it is difficult to obtain reservoir samples. These data shed light on a possible trapping mechanism caused by fluids in place. The study also used several methods and tools to confirm the conclusions and to ensure repeatability of results.

Cyclotron resonance in HgCdTe-based heterostructures in strong magnetic fields

Cyclotron resonance (CR) study of HgCdTe-based quantum wells with both inverted and normal band structures in quantizing magnetic fields was performed. In normal-band sample in addition to electron CR transitions a strong absorption line presumably related to impurity transitions was discovered. Anticrossing of electron and hole Landau levels was observed in inverted-band sample. In semimetallic HgTe quantum wells with inverted band structure, a hole CR line was observed for the first The obtained results were interpreted within the Kane 8 × 8 model, the valence band offset of CdTe and HgTe, and the Kane parameter EP being adjusted.

Numerical Studies of Ponderomotive Acceleration and Ion Cyclotron Resonance: Application to Next Generation Electric Thrusters

We have examined ponderomotive acceleration/ion cyclotron resonance (PA/ICR) of argon ions by performing test particle simulations. The PA gives rise to the pure parallel acceleration of ions, while the ICR causes the perpendicular ion heating followed by the energy conversion from the perpendicular to the parallel direction in the presence of a divergent background magnetic field. The energy gain by the PA/ICR is classified in terms of the adiabatic parameter, Λ = LBΩ0/v0||, where LB is the axial divergent scale length of the background magnetic field, Ω0 is the ion gyrofrequency at the resonance, and v0|| is the initial ion drift velocity along the axial magnetic field. For Λ 100, Δ saturates since the increased axial velocity of the ion via the PA reduces the transit time to cross the acceleration region. When the externally applied rf electric field intensity is increased to 1000 V/m, we find a maximal 60% increase in the energy gain for the PA/ICR scheme compared with the energy gain by the ICR only. We have applied the PA/ICR scheme to the next-generation electric thruster, and have estimated the thrust including ion wall-loss and ion-neutral collisions. c © 2013 The Japan Society of Plasma Science and Nuclear Fusion Research

Cyclotron resonance study in InAs/AlSb quantum well heterostructures with two occupied electronic subbands

We report on the cyclotron resonance (CR) study in InAs/AlSb (001) quantum well (QW) heterostructures with two occupied electronic subbands. Experimental results are compared with the CR energy calculations in the self-consistent Hartree approximation. Our theoretical approach is based on the 8-band k · p Hamiltonian and takes into account the band nonparabolicity, lattice-mismatch deformation, and spin-orbit coupling. We find out a large splitting of CR line associated with a difference in cyclotron energies in the first and second electronic subbands. The results of CR study in InAs/AlSb QW heterostructures reveal pronounced effect of the “built-in” electric field on CR spectra in the samples with two occupied electronic subbands.

Many-body corrections to cyclotron resonance in graphene

We report our recent study of cyclotron resonance in graphene, with focus on the many-body effect on the resonance energies. The genuine many-body corrections turn out to derive from vacuum polarization, specific to graphene, which diverges at short wavelengths and which requires renormalization of velocity and, for bilayer graphene, interlayer coupling as well. As a result, the renormalized velocity and interlayer coupling strength run with the magnetic field, and many-body corrections are uniquely determined from one resonance to another. Theory is compared with the experimental data for both monolayer and bilayer graphene.

Compact magnetospectrometer for pulsed magnets based on infrared quantum cascade lasers

In this paper we present a portable quantum cascade laser (QCL) based infrared magnetospectrometer covering the spectral range from 5 to 120 μm. The variation of the excitation wavelength is enabled by an easy change of the QCL plug-in modules, while the use of any other external source is also possible. The performance of the setup is illustrated via cyclotron-resonance studies under pulsed magnetic fields up to 60 T.

Quantum Transport and Cyclotron Resonance Study of Ge/SiGe Quantum Wells in High Magnetic Fields

Shubnikov-de Haas oscillation and cyclotron resonance were studied for high mobility p-type Ge channels in strained Ge/Si1−xGex quantum wells, using pulsed high magnetic fields up to 50 T. Fine quantum oscillations were observed in ρxx. Reflecting the complex Landau level structure in the nearly degenerate valence bands, the Fourier transform of the oscillatory spectra consists of several peaks. Cyclotron resonance was measured at photon energies between 10 and 17 meV. Two well-defined resonance peaks were observed in two samples with different x, resulting in different strains. A large non-parabolicity and large strain dependence of the effective masses were observed.

Cyclotron resonance in P-doped InSb quantum wells

A combined experimental and theoretical study of cyclotron resonance was conducted on a two-dimensional hole system in an InSb quantum well, which was 9 nm thick and compressively strained by ∼0.65%. An effective mass of 0.065mo and a g-factor |g∗|≈23 were deduced from cyclotron resonance features at magnetic fields of 2.5 T and 6 T, respectively, when the InSb quantum well had a hole density of 3.5×1011 cm−2. At higher magnetic fields, separate cyclotron resonances are observed for different spin-conserving transitions. The magnetic field dependences of the effective mass and g-factor for holes are well explained by an 8-band Pidgeon-Brown model generalized to include the effects of the confinement potential and pseudomorphic strain.

Effect of low nitrogen concentrations on the electronic properties ofInAs1−xNx

We report cyclotron resonance (CR), transverse magnetoresistance (MR), and Hall effect studies of a series of $n$-type ${\text{InAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ epilayers grown on GaAs with $x$ up to 1%. The well-resolved CR absorption lines, the classical linear MR, Shubnikov--de Haas magneto-oscillations, and negative MR revealed in our experiments provide a means of probing the effect of the N atoms on the electronic properties of this alloy system and reveal qualitative differences compared to the case of the wider gap III-N-V compounds, such as ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$. In ${\text{GaAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ electron localization by N levels that are resonant with the extended band states of the host crystal act to degrade the electrical conductivity at small $x$ $(\ensuremath{\sim}0.1%)$. These phenomena are significantly weaker in ${\text{InAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ due to the smaller energy gap and higher energy of the N levels relative to the conduction band minimum. In ${\text{InAs}}_{1\ensuremath{-}x}{\text{N}}_{x}$ the electrical conductivity retains the characteristic features of transport through extended states, with electron coherence lengths (${l}_{\ensuremath{\varphi}}\ensuremath{\sim}100\text{ }\text{nm}$ at 2 K) and electron mobilities ($\ensuremath{\mu}=6\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }{\text{cm}}^{2}\text{ }{\text{V}}^{\ensuremath{-}1}\text{ }{\text{s}}^{\ensuremath{-}1}$ at 300 K) that remain relatively large even at $x=1%$.

BAND STRUCTURE AND ELECTRON VELOCITY MEASUREMENT IN CARBON NANOTUBES AND GRAPHENE

We discuss recent measurements of the interband spectrocopy of carbon nanotubes and studies of cyclotron resonance in graphene, using these to examine the possible dependence of the band structure of graphene on the number of layers present and the role of Coulomb interactions. Cyclotron resonances gives a value for the electron velocity at the Dirac point of 1.093×106 ms-1, which is ~ 20% larger than would be expected from deductions of the band structure of carbon nanotubes. In addition, a significant asymmetry exists between band structure for electrons and holes, which gives rise to a 5% difference between the velocities at energies of 125 meV away from the Dirac point.

Chemistry of (and on) Transition Metal Clusters: A Fourier Transform Ion Cyclotron Resonance Study of the Reaction of Niobium Cluster Cations with Nitric Oxide

The reactions of niobium cluster cations, Nb(+)(n) (n = 2-19), with nitric oxide have been investigated using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR). The overall reaction rate constants are found to be in reasonable agreement with collision rates calculated using the surface charge capture model. The dominant reaction for small clusters (n <9) involves reaction-induced fragmentation resulting in the loss of either NbO or NbN. By contrast, the main reaction observed for the larger clusters (n> 11) is sequential NO chemisorption. Clusters n = 9, 10 exhibit both extremes of behaviour and are the only clusters upon which there is evidence of NO decomposition with N(2) loss observed whenever multiple NO molecules are co-adsorbed. The rate constants for each process have been determined as a function of cluster size.

Radical cation/radical reactions: A Fourier transform ion cyclotron resonance study of allyl radical reacting with aromatic radical cations

A method for the study of reactions of open-shell neutrals (radicals) and radical cations is described. Pyrolysis (25–1500 °C) of thermally labile compounds, such as, 1,5-hexadiene via a Chen nozzle yields a seeded beam of reactive species in helium. The pyrolysis products are then analyzed by electron ionization (EI) or reacted with stored ions. Electron ionization of the pyrolysis products of 1,5-hexadiene shows that both the allyl radical and allene are generated. Reactions of benzene radical cations and the pyrolysis products of 1,5-hexadiene result in carbon–carbon bond formation. Those reactions of allyl radical with the benzene radical cation yield the C 7H 7 + ion of m/ z 91, permitting an unusual entry into arenium ions. The reaction of allene with benzene radical cation in contrast yields C 9H 10 + and C 9H 9 +.

Cyclotron resonance of electrons and holes in graphene monolayers

We report studies of cyclotron resonance in monolayer graphene. Cyclotron resonances are detected by observing changes in the photoconductive response of the sample. An electron velocity at the Dirac point of 1.093 x 10(6) m s(-1) is obtained, which is the fastest velocity recorded for all known carbon materials. In addition, a significant asymmetry exists between band structure for electrons and holes, which gives rise to a 5% difference between the velocities at energies of 125 meV away from the Dirac point.

Cyclotron resonance study of the electron and hole velocity in graphene monolayers

We report studies of cyclotron resonance in monolayer graphene. Cyclotron resonance is detected using the photoconductive response of the sample for several different Landau level occupancies. The experiments measure an electron velocity at the $K$ (Dirac) point of ${c}_{K}^{*}=1.093\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.3em}{0ex}}\mathrm{m}\phantom{\rule{0.2em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, which is substantially larger than in thicker graphitic systems. In addition we observe a significant asymmetry between the electron and hole bands, leading to a difference in the electron and hole velocities of 5% by energies of $125\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ away from the Dirac point.

Optically detected cyclotron resonance studies of InxGa1−xNyAs1−y∕GaAs quantum wells sandwiched between type-II AlAs∕GaAs superlattices

We report on our results from a systematic study of layered structures containing an InGaNAs∕GaAs single quantum well (SQW) enclosed between staggered type II AlAs∕GaAs superlattices (SL), by the photoluminescence (PL) and optically detected cyclotron resonance (ODCR) techniques. Besides the ODCR signal known to originate from electrons in GaAs, the predominant ODCR peak is shown to be related to carriers with a two-dimensional character and a cyclotron resonance effective mass of m*≈(0.51–0.56)m0. The responsible carriers are ascribed to electrons on the ellipsoidal equienergy surface at the AlAs X point of the Brillouin zone within the SL, based on results from angular and spectral dependences of the ODCR signal. No ODCR signal related to the InGaNAs SQW was detected, presumably due to low carrier mobility despite the high optical quality. Multiple absorption of photons with energy below the band gap energy of the SL and the GaAs barriers was observed, which bears implication on the efficiency of light-emitting devices based on these structures.

Confined-acoustic-phonon-assisted cyclotron resonance in free-standing semiconductor quantum well structures

Phonon-assisted cyclotron resonance (PACR) in a free-standing quantum well (FSQW) structure is studied when electrons are scattered by confined-acoustic modes through deformation potential. Elastic continuum model is employed to describe the confined-acoustic modes, that are classified as shear, dilatational, and flexural waves. Expression for the absorption coefficient is obtained. Numerical results are presented for the frequency, magnetic field, temperature, and well-width dependence of absorption coefficient in $\mathrm{GaAs}$ and $\mathrm{GaN}$ free-standing quantum well structures. In the extreme quantum limit only dilatational modes contribute for phonon-assisted cyclotron resonance. Results are compared with those based on bulk description of acoustic phonons and significant differences are noted. The calculations demonstrate that phonon-assisted cyclotron resonance studies can lead to a better understanding of confined electron-acoustic phonon interaction in free-standing quantum wells.

Understanding of the Structure, Bonding, Formation and Decomposition of Metalloid Aluminum Clusters—A Fourier Transform Ion Cyclotron Resonance Study of Solid AlCp*

The investigation of the tetrahedral Al4Cp*4 cluster with Fourier transform ion cyclotron resonance mass spectrometry using laser desorption /ionization as the ionization method results in a couple of aluminum cluster compounds AlxCp*+y (x > y) with up to eight aluminum atoms. MS(n) experiments are performed in order to understand the formation and reactivity of the different species. Quantum chemical calculations of the structure and energy for all compounds identified complete this study.

Ultrahigh-field hole cyclotron resonance absorption inIn1−xMnxAsfilms

We have carried out an ultrahigh-field cyclotron resonance (CR) study of $p$-type ${\mathrm{In}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ films, with $\mathrm{Mn}$ composition $x$ ranging from 0 to 2.5%, grown on $\mathrm{GaAs}$ by low-temperature molecular-beam epitaxy. Pulsed magnetic fields up to $500\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ were used to make cyclotron resonance observable in these low-mobility samples. Clear CR spectra have been observed for all the samples at high fields in the megagauss range and even at room temperature. It was found that the observed cyclotron masses are not significantly dependent on the $\mathrm{Mn}$ concentration, indicating a large number of itinerant, effective-mass-$p$-type holes rather than $d$-like holes exist. It further suggests that the $p\text{\ensuremath{-}}d$ exchange mechanism is more favorable than the double exchange mechanism in this narrow gap $\mathrm{InAs}$-based dilute magnetic semiconductor. In addition to the fundamental heavy-hole and light-hole cyclotron resonance absorption appearing near the high-magnetic-field quantum limit, we observed many inter-Landau-level absorption bands whose transition probabilities are strongly dependent on the sense of circular polarization of the incident light. It has been found that the detailed theoretical calculation in terms of the effective mass theory explains the most of the CR spectra quantitatively, including the polarization dependence.